Transmission clutches with fully-resetting modulator-load-piston

ABSTRACT

A multi-functioning hydraulic transmission control circuit including interacting valve mechanism parts which, in response to a shift being called for in a clutch-cylinder-controlled multi-speed transmission, inaugurate a fill pressure flow to the clutch cylinders concerned, prior to the subsequent fluid pressure rise effected therein; thereafter, upon completion of the fill, the parts modulate pressure rise of the hydraulic clutch fluid from and at approximately actual clutch fill pressure up to, and remaining at, the final pressure of engagement. 
     These functions including full resetting of the parts at the beginning of each shift, and a lesser and a least gradual pressure rise afforded during respective second and third speed upshifts, are all accomplished by and among a pair of direction-selector and orificed-speed-selector valve spools connected to the transmission clutch cylinders to direct valve fluid output thereto selectively, and also 1st, dump valve, 2d, simulated clutch piston, 3d, load piston, 4th, modulator valve, and 5th, interacting spring parts collectively providing said directed valve fluid output, all in a valve bore common thereto, and arranged therein with the dump valve part confronted at one side by the simulated clutch piston part so as to define mutually therewith a differential pressure chamber in the bore, and confronted at the other side by a first side of the load piston part so as to define mutually with that first side a signal pressure chamber in the bore, and with an opposite side of the load piston part spacedly confronting the modulator valve part so that they mutually engage therebetween the interacting spring parts in the common bore.

The present case (this application) is a division of my application Ser.No. 693,469, filed June 7, 1976, now U.S. Pat. No. 4,135,610 (parentpatent).

All of the claims in this application are directed to non-electedsubject matter which was divided from the parent patent. Thisapplication's disclosure is the same disclosure of my prior U.S. Pat.No. 4,132,302 (continuing patent) which is a continuation-in-part of theparent patent. All of the claims in the continuing U.S. Pat. No.4,132,302 include limitations directed to the improvements shown inFIGS. 2 and 8 of this application, which improvements are not disclosedin the parent patent. The claims of this application do not include saidimprovements.

The present invention relates to hydraulic controls for smoothlyeffecting shifting of a vehicle transmission of the type in which theshifting power is provided by hydraulic pressure applied in thetransmission itself, i.e., to effect a smooth power-shift.

It more specifically relates to a multi-functioning hydraulictransmission control circuit including interacting valve mechanism partswhich, in response to a shift being called for in aclutch-cylinder-controlled multi-speed transmission, inaugurate a fillpressure flow to the clutch cylinders concerned, prior to the subsequentfluid pressure rise effected therein; thereafter, upon completion of thefill, the parts modulate pressure rise of the hydraulic clutch fluidfrom and at approximately actual clutch fill pressure up to, andremaining at, the final pressure of engagement.

The above parts, which shift position either directly or indirectly inresponse to position changes made to a transmission shift lever by anoperator, comprise 1st speed selector and 2d direction selector valvespools connected to the transmission clutch cylinders to direct valvefluid output thereto selectively, and also 3d dump valve, 4th a loadpiston, 5th another piston, 6th a modulator valve, and 7th interactingspring parts collectively providing said directed valve fluid output,all in a bore common thereto, and arranged therein with the dump valvepart confronted at one side by the other piston part, 5th above, so asto define mutually therewith a differential pressure chamber in thebore, and confronted at the other side by a first side of the loadpiston part so as to define mutually with that first side a signalpressure chamber in the bore, and with an opposite side of the loadpiston part spacedly confronting the modulator valve part so that theymutually engage therebetween the interacting spring parts, 7th above, inthe common bore.

Background patents include but are not limited to U.S. Pat. Nos.3,033,333, 3,125,201, 3,181,385, 3,352,392, 3,444,968, 3,498,150,2,935,999, 3,583,422, 3,618,424, 3,882,738, 3,991,865, 3,998,111,4,000,795, and 4,046,162.

According to past transmission practices in tractors and other vehiclesin connection with controlled rate of rise valve assemblies eachincluding a modulator valve and an associated load piston therefor, thespeed and direction clutches provided in the transmission have beenoperated through the controlled rate of rise valve assembly to cushionclutch engagement. In tractor transmissions affording multi-speed rangesboth forward and reverse, it is neither necessary nor desirable that thepressure rise be as gradual in other transmission speed settings asidefrom the high torque, first speed which tends to engage jerkily. Inother words as soon as it is upshifted out of first, a transmissionworks at a disadvantage without having a lesser and a least gradualpressure rise afforded during its respective second and third speedupshifts. And all the more it is a disadvantage that the rate of risevalve assembly is hydraulically spaced a long distance away from thetransmission controlled thereby so that the valve assembly in a senseoperates too remotely from, and altogether ignorantly of, the actualclutch fill pressure existing in the transmission itself. The latterdisadvantage manifests itself in the functioning of the modulator valveand load piston in some cases, with the load piston never fullyresetting itself, whereupon the subsequent fluid pressure rise starts ata point appreciably higher than actual clutch fill pressure in thetransmission itself and so no smooth, gradual shift results.

According to my invention, the foregoing disadvantages and drawbacks arematerially reduced in severity if not eliminated altogether, because thefunctions including full resetting of the parts at the beginning of eachshift, and a lesser and a least gradual pressure rise afforded duringrespective second and third speed upshifts, are all accomplished by andamong the novelly coacting parts hereinabove enumerated. One preferredway for such accomplishment resides in the present provision of asimulated clutch piston serving in the rate of rise valve assembly asthe other piston, 5th above, and in the present provision of an orificedvalve passage in the bore housing progressively opened between the speedselector valve spool, 1st above, and the signal pressure chamber in theaforesaid common bore, all as will now be explained in detail.

Features, objects, and advantages will either be specifically pointedout or become apparent when, for a better understanding of theinvention, reference is made to the following description taken inconjunction with the accompanying drawings which show a preferredembodiment thereof and in which:

FIG. 1 is a schematic showing of a three speed forward, three speedreverse transmission and hydraulic power control system therefor, withthe rate of rise valve assembly of the present invention forming part ofthe control system shown;

FIGS. 2, 3, 4, and 5 are all enlarged cross sectional views of the rateof rise valve assembly of the invention, the same as appears as a detailin FIG. 1 and with the components shown in FIGS. 2-5 in the variousoperating positions specified under appropriate subheadings hereinafter;

FIG. 6 is an isometric view of an hydraulic load piston appearing inlongitudinal cross section in each of the foregoing figures;

FIG. 7 is a graphical representation of a portion of pressure tracesdesirably and undesirably associated with the operation of the controlsystem foregoing:

FIG. 8 shows a flow-check valve as used in the invention, in actualpractice; and

FIG. 9 is a graphical representation of complete pressure tracesassociated with the operation.

More particularly in the drawings, a reversible, power shifttransmission 10 controlled in accordance with my invention is shown inFIG. 1 having three speeds in the forward range and three speeds in thereverse range. The transmission 10 has hydraulically operated, clutchunits controlled first by a piston and cylinder 1, and similarly by 2,3, F, and R for power shift operation. In one of the standard ways, theclutch units controlling 1, 2, and 3 speeds are in the forward sectionof gearing, whereas the units controlling direction F-R are in theoutput section of the transmission 10.

Located forwardly of the transmission 10 are an engine driven hydraulicpump 12, and an engine driven torque converter 14 coupled to thetransmission 10 to provide torque-amplified input thereto.

Hydraulic drainage from various drains denoted D is collected in atransmission sump 16, from which it is drawn through a pump intake line18 into the inlet side of the hydraulic pump 12. From its pump outputside, the pump 12 discharges hydraulic fluid through an outlet line 20and a filter 22, thence into a pump pressure line 24 at pressure P.

Pump line pressure P enters a rate of rise valve assembly housing 26through a modulating pressure chamber conduit 28, through a modulatedbore core conduit 30, and through a rate of rise valve modulation borerestriction which is a large, fixed clutch-fill orifice 32 forming aseparate part of a rate of rise valve assembly modulation bore 34 andfeeding valve output pressure P1 into a housing tee 36.

The tee 36 on the downstream side of the modulation bore restriction 32splits into lower and upper branches as viewed in FIG. 1. Hydraulicfluid under a valve modulated first output pressure P1 flows through thelower branch into a speed valve output connection 38. In the upperbranch, hydraulic fluid originally under pressure P1 is supplied to adirection valve output connection 40 at a valve modulated secondpressure P2 by way of a neutralizer valve bore 42 occupied at one end bya neutralizer valve spool 44.

In the valve housing 26, in a speed valve bore 46 interposed in thespeed valve output connection 38, a three-position speed valve spool 48is reciprocally positioned by the operator to selectively supply valvemodulated first output fluid to a set of individual speed lines 50leading to each one of the pistons and cylinders 1, 2, 3 of the clutchunits in the forward section of the transmission 10. Each line 50 is along one and, due to friction and restriction therein, the actual clutchpressure PA of the clutch units will be substantially less than thevalve modulated first output pressure P1.

Similarly, in a direction valve bore 52 interposed in the directionvalve output connection 40, a three-position direction valve spool 54 isreciprocally positioned by the operator to selectively supply valvemodulated second output fluid at pressure P2 to a pair of individualdirection lines 56 leading to pistons and cylinders F, R of the clutchunits in the output section of the transmission 10. Due to hydraulicfriction and restriction in each of the direction lines 56 which afforda long and somewhat tortuous path to flow of hydraulic fluid therein,actual pressure PA in the piston and cylinder F and in the piston andcylinder R will be substantially less than the pressure P2 in thedirection valve output.

TORQUE CONVERTER--FIG. 1

In the operation of the hydraulic system for torque amplification,hydraulic fluid keeps the torque converter 14 filled, being arrangedwith its supply of fluid provided by a rate-of-rise-pressure modulatingvalve 58 located in the right end of the rate-of-rise valve assemblymodulation bore 34, and with its back pressure maintained by a torqueconverter regulator valve spool 60 reciprocal in the left end of theneutralizer valve bore 42. More particularly, a back pressure land 62 onthe spring seated spool 60 is operatively located between a second coregroove 64 and a first core groove 66 connected to a converter outletline 68. As hydraulic pressure rises between the end of the spool 60 andthe left end of the bore 42 against which it is seated, the spool 60moves rightwardly in response to this increasing converter backpressure, and the intervening land 62 thereon opens andintercommunicates the first bore groove 66 and the second bore groove64, which latter discharges the excess hydraulic fluid therefrom througha cooler inlet line 70, an hydraulic torque converter cooler 72, acooler outlet line 74, and a housing oil gallery 76, thence into atransmission lube system L and ultimately into the transmission sump 16.

The rate-of-rise-pressure modulating valve 58 and a torque converterinlet line 78 provide a direct connection between the modulated borecore conduit 30 and the torque converter 14 on its inlet side. Moreparticularly, in the rate of rise valve assembly modulation bore 34,which bore is divided into the respective differential pressure chamber80, signal pressure chamber 82, spring chamber 84, and modulatingpressure chamber 86 as viewed in that order from left to right in FIG.2, the modulating valve 58 is of piston shape and is oriented with itspiston end hydraulically separating the spring chamber and modulatingpressure chamber 84 and 86 in the bore 34.

At the times while it is maintaining the system under full clutchengaging pressure, the modulating valve 58 has an intermediate openposition as shown in solid lines in FIGS. 1 and 2, having been moved bypressure in the modulating pressure chamber 86 to a point where thehydraulic pressure is exactly equal to and balanced by a partiallycompressed spring group 88 pressing against the inside of the valvepiston end. In that intermediate position shown, a regulating valve land90 maintains the pump pressure P in a bore core 92 by controlling flowof excess fluid into a bore core 94 thence to the torque converter (notshown in FIG. 2) through the torque converter inlet line 78. Additionalpressure encountered in the modulating pressure chamber 86, as due tostiff, very cold oil, will bring about progressive leftward openingmovement of the valve 58 causing cooperation between a bore core 96connected to drain D and a dual function dump land 98 on the valve 58.The dump land 98 has a valve edge at the right as viewed in FIG. 2 whichuncovers core 96 and provides a first function whereby oil from thecores 92 and 94 will go directly to the bore core 96 and drain D, atleast until the oil warms up in the system. The dump land 98 also hasports 100 performing the second function, in all positions of the valve58, of continuously venting the spring chamber 84 to drain D by way ofthe core 96. A shoulder 102, formed on the valve 58 adjacent a valveseating spring 104, engages the fixed seat for spring 104 and limitsprogressive valve opening movement to a relatively short amount ofoverall valve travel.

An intermediate guide and seat 106 aligns inner ones of the springs ofthe spring group 88 which are connected thereby to act in tandem withinthe spring chamber 84.

The spring group 88 and associated parts within the rate of rise valveassembly modulation bore 34 form a rate of rise valve assembly generallyindicated at 108 and described in detail shortly.

SPEED VALVE--FIG. 1

When the spool 48 in the speed valve bore 46 is detented at 110 in thefirst or 1 speed position as shown in solid lines, the speed lines 50 tothe respective piston and cylinder units 2 and 3 are connected by thespool 48 in readily discernible paths to drain D; at the same time fromthe output connection 38 in which the speed valve is located, the valvemodulated first output pressure P1 through a short conduit 112 isadmitted by an open spool land 114 into an individual speed line 50 andthe clutch piston and cylinder 1 so as to prepare the transmission 10for first speed drive.

Progressive inward movement of the speed valve spool 48 rightwardly soas to assume an intermediate or 2 position, causes the piston andcylinder 1 and 3 to be connected by the spool 48 to drain D; at the sametime valve modulated first output pressure P1 from the output connection38 and a core groove 116 is admitted by an open spool land 118 into theappropriate speed line 50 thence into piston and cylinder 2 to preparethe transmission 10 for second speed drive. Also at the same time, asecond branch source of the fluid system output is opened under pressureP1 to supply fluid therefrom to the signal pressure chamber 82; morespecifically, spool land 120 uncovers the mouth of a first auxiliarypassage 122 interconnecting the short output conduit 112 and the signalpressure chamber 82 so as to provide a first supplement to the flow offluid in the latter for a reason later to be disclosed. That same spoolland 120 upon further depression of the spool 48 to extreme rightwardposition corresponding to speed 3, uncovers the mouth of a secondauxiliary passage 124 between the short output conduit 112 and thesignal pressure chamber 82 to afford a second supplement to the flow ofhydraulic fluid into the latter.

When the spool 48 is fully depressed rightwardly for the speed 3condition, the clutch piston and cylinder units 1 and 2 are connected todrain D; at that time, the spool land 120 uncovers and leaves open acore groove 126 to pressure P1 in the short output conduit 112, so as topressurize the clutch piston and cylinder 3 and prepare the transmission10 for speed 3 condition.

DIRECTION VALVE--FIG. 1

When the spool 54 in direction valve bore 52 is detented at 128registering at position F for forward drive as shown by solid lines, thevalve modulated second output pressure P2 which enters first a coregroove 130 and thereafter a direction valve bore 52, is directed by aspool land 132 into the appropriate individual direction line 56 andintroduced by the latter into the piston and cylinder F to completeforward drive in the transmission. The individual line 56 to the clutchpiston and cylinder R is meantime connected by the spool 54 in a pathleading through the hollow core 134 of the latter, past the detent 128,and thence to drain D in the transmission 10 whereby the clutch cylinderis kept inactive.

When the direction valve spool 54 is partway depressed into anintermediate position corresponding to N to neutralize the transmission10, the pressurized core groove 130 of direction valve bore 52 isblocked off by the spool land 132 and by an adjacent land 136, whereasboth direction lines 56 are connected to drain D in discernibledirection valve paths in FIG. 1. So the direction clutches aredisengaged and no drive is transmitted through the transmission 10.

Finally upon full depression of the spool 54 into its extreme positioncorresponding to the R condition of the transmission for reverse, thespool land 136 directs pressure P2 from the core groove 130 into a coregroove 138, whence the pressure P2 is communicated through theappropriate direction line 56 into the clutch piston and cylinder R,completing the reverse path through the transmission 10. At the sametime, the direction line 56 to the clutch piston and cylinder F forforward drive is connected by the spool 54 in a path including thehollow core 134, past the detent 124, thence to drain D so as to keepthe transmission forward drive inactive.

NEUTRALIZER--FIG. 1

The neutralizer valve spool 44, which in a rightward position has acondition of repose as shown, and which has a controlled, shiftedposition to the left as viewed in FIG. 1, is under the electro-hydrauliccontrol of a brake operated, transmission neutralizer contacts component140, an electric neutralizer valve solenoid 142, and an hydraulicneutralizer valve component 144, all forming parts of a three-waycartridge solenoid valve assembly generally indicated at 146. The valveassembly 146 is in turn controlled by the vehicle brake pedal 148 in away automatically to neutralize the transmission 10 at all times duringwhich the vehicle brakes are applied.

During normal vehicle running conditions, the neutralizer valve spool 44occupies its rightward or repose position, and so do the brake pedal 148and valve assembly 147, all as shown in solid lines in FIG. 1. Duringsuch condition of repose, a spool groove 150 on valve spool 44, a spoolgroove 152 on valve component 144, and an interaction spring 154 betweenthe torque converter regulator valve spool 60 and the neutralizer valvespool 44 urging them to seat in opposite ends of the bore 42, areperforming as follows. The spool groove 150 completes an hydraulic pathbetween the housing tee 36 and direction output connection 40;therefore, the valve modulated first and second output pressures P1 andP2 are equal to one another, enabling the selected ones of the speed anddirection clutches to remain operative so that the transmission 10 staysengaged. The spool groove 152 completes an hydraulic path leading fromthe end of the bore 42 occupied by the corresponding end of theneutralizer valve spool 44, through a neutralizer valve line 156, thenceinto the groove 152, and a pair of series connected drain lines 158 and160 leading to drain D in transmission 10. So the unopposed spring 154holds the neutralizer spool 44 in its unshifted position of repose asshown in solid lines in FIG. 1, allowing the transmission 10 to continueto drive in the direction and speed settings selected.

However, depression of the brake pedal 148 into the broken line positionshown, not only applies the vehicle brakes by conventional means, notshown, but also moves a switch arm counterclockwise as viewed in FIG. 1closing the transmission neutralizer contacts component 140 and settingthe transmission 10 in neutral. More particularly, contact closing inthe battery solenoid circuit illustrated electromagnetically causes thevalve solenoid component 142 to rise as viewed in FIG. 1 and to shiftupwardly the spool groove 152 therewith. Therefore, the modulatingpressure chamber 86 at pressure P is interconnected by way of a pressureline 162 with the spool groove 152, and at the same time the neutralizervalve line 156 is connected with the same spool groove 152, thuspressurizing that end of the valve bore 42 which is occupied by thecorresponding end of the neutralizer spool 44.

Accordingly, against the resistance of spring 154, the neutralizer spool44 is pressure actuated under pressure P into its shifted position, tothe left as viewed in FIG. 1; the neutralizer spool groove 150interconnects the direction valve output connection 40 and drain D,whereas pressure P1 from the housing tee 36 is blocked off by the mainportion of the neutralizer spool 44. Hence, the F-R direction clutchunits are disengaged, interrupting the transmission of power intransmission 10 always contemporaneously with brake application. So thevehicle brakes engage to stop motion or to arrest motion of the vehicleto the degree desired, without having to overcome traction power of theengine as well.

RATE OF RISE VALVE ASSEMBLY--FIG. 3

Forming part of the rate of rise valve assembly 108, a load piston 164is controlled by hydraulic pressure of signal pressure chamber 82 and bymechanical pressure of the spring group 88 either to perform a resettingstroke in the bore 34 in the direction of an arrow 166, and to perform aloading, opposite reciprocal stroke to the right as viewed in FIG. 3.The piston 164 has a crown head which is formed with a shallow centralrecess 168 and which is subject to signal pressure S, and has the springgroup 88 seated inside the head so as to interact with the modulatingvalve 58 by reacting thereagainst and loading it for the desired rate ofrise modulation.

About the load piston 164, a uniplanar ring includes four spaced apartcontrol edges 170 on the piston that establish cooperation with twodrain connected bore ports 172, which ports are in the path ofreciprocation of the piston 164 and which are uncovered by the controledges 170 during piston movement to the right as viewed in FIG. 3.

Thus, during its loading stroke, the load piston 164 will stop moving tothe right and end the stroke at the point where it uncovers drain ports172, because immediately the activating pressure S thereon will startbeing vented to drain at 172. Conversely, piston travel for resetting inthe direction of the arrow 166 is limited as the piston 164 stopsimmediately upon contact with, or in practice just short of, the dumpvalve 174 of an adjacent signal pressure control assembly 176.

DUMP VALVE--FIG. 4

As viewed in FIG. 4, the dump valve 174 will be appreciated to haveprimary control over the emptying and filling of chamber 82. That is,leftward movement of the dump valve 174 opposite to the direction of anarrow 178 will vent the signal pressure chamber 82 through a bore core180 to drain, tending to empty the chamber. But movement of the dumpvalve 174 in the direction of the arrow 178 causes a sealing edge 182thereof to seal off an adjacent land 184 in the bore 34 and allow aconstant differential, constant flow, timing orifice 186 fixed in thecenter of the dump valve 174 to fill the signal pressure chamber 82. Thedump valve cavity pressure C within the differential pressure chamber 80causes essentially one way flow through the fixed orifice 186.

Within the dump valve cavity, a sleeve 188 is fixed and provides theseat for a light spring 190 urging the dump valve 174 to its sealedclosed position in the direction of the arrow 178. The head of the valve174 incorporates a pressure equalizing groove formation 192 to keep thevalve centered and free from binding.

CLUTCH FILL PISTON--FIG. 5

Within the fixed sleeve 188 of the signal pressure control assembly 176,a simulated clutch fill piston 194 is reciprocally mounted to moverightwardly in the direction of an arrow 196 to an extreme positionlimited by a cross pin 198 fixed in the rate of rise valve assemblyhousing 26, or to move leftwardly opposite to the arrow's direction andbottom itself against the adjacent portion of the housing 26.

The dump valve 174 is in sole control of directing fluid to fill and toempty the piston cavity 200 of piston 194. In the valve-closed positionof the dump valve 174 as shown in FIG. 5, a dump valve land 202 divertsvalve cavity pressure C from the differential chamber 80 through a borecore 204 leading to the back of the piston, thence into a passage 206and the piston cavity 200. Pressure is thus equalized across the piston194 enabling a light spring 208 inside the head of the piston to movethe latter on a complete resetting stroke in the direction of the arrow196. But when the dump valve 174 is in the dump position to the left ofthe position as shown in solid lines in FIG. 5, the valve land 202 ventsthe bore core 204 through the bore core 180 to drain D, enabling thevalve cavity pressure C of the differential pressure chamber 80 toovercome the light spring 208 and force the piston 194 leftwardly asviewed in FIG. 5 on a complete control stroke terminating in the solidline position shown.

STEADY STATE CLUTCH ENGAGEMENT--FIG. 2

C is equal to P1, P1 is equal to P, and P is 30 psi greater thanpressure S, according to this dynamic equilibrium condition as shownhere. The condition can be accurately mechanically set, in view of thespring chamber 84 always being maintained in drain pressure condition,also in view of the flow through the rate of rise valve modulation borerestriction or clutch fill orifice 32 being inconsequential when theclutches are fully engaged, and finally in view of the strategicplacement of the spring group 88 in the spring chamber and of the valveseating spring 104 engaging the head of the rate of rise pressuremodulating valve 58.

More particularly, in spite of smallness or the magnitude of flow in thedirection of the arrow through the restrictive timing orifice 186, thespring group 88 is precisely calibrated so that the active one of thefour control edges 170 will restrict outflow from the bore ports 172constituting drain holes to the same restricted rate, thus maintainingthe signal pressure S in chamber 82 at a constant regulated value, e.g.,270 psi (18.4 Atmos.). On the other hand, the valve seating spring 104which is precalibrated to a moderate value, such as the equivalent to 30psi, will act in conjunction with the same spring group 88 having theequivalent of 270 psi (18.4 Atmos.) pressure, to cause rate of risepressure modulating valve 58 to regulate by means of the valve land 90thereon with the total of 300 psi (flat curve segment at level of andadjacent "300 P1," FIGS. 7 and 9, equivalent to (20.4 Atmos.) as thepressure P. Because as noted, P equals P1 equals C, cavity pressure C inthe differential chamber 80 will maintain constant flow through therestricted fixed orifice 186 creating the 30 psi pressure dropconsistent with the signal pressure S remaining at 270 psi (18.4Atmos.).

The restrictive flow through the timing orifice 186 making its way outthe drain holes 712 plus the regular leakage in the selected clutch ofeach of the two clutch groups amounts in total to a relatively minorflow. The corresponding minor flow through the large, clutch fillorifice 32 generates a barely perceptible pressure drop thereacrossallowing pressure P and P1 to equalize.

DUMP, INITIATING CLUTCH FILL--FIG. 3

Fill time is so comparatively short in a shift cycle of thetransmission, that the problem is to reduce the dump valve cavitypressure C to a low point and in turn reduce the signal pressure S to alow point, such that the resetting load piston 164 moving in thedirection of the arrow 166 will be able fully to complete the resettingstroke before the fill portion of the clutch cycle can elapse. Thecomplicating aspect is that the pressure P1 of the valve output fluidwhich restrictively enters the dump valve cavity of which the pressureis C, must have a value of about 50 psi in order that, at the clutchitself, the effective pressure PA actually filling the clutch will beabout 20 psi. That is, P1 on which S ultimately depends, iscomparitively too high for S's purposes. The tendency which thereforemust be overcome is that the signal pressure S will be too high when,preferably, it should be at or about actual clutch fill pressure of 20psi so as not unduly to oppose full reset of the load piston 164.

In approaching the present solution to the problem, let it be assumed ashift is being made with the transmission in first gear and with thechange, to be made, being made in the direction clutches, e.g., fromreverse R to forward F. Hence, the clutch piston and cylinder unit 1will remain filled whereas the clutch piston and cylinder unit F, notshown, will be empty and require complete filling. So all pressures inthe system will drop drastically because 20 psi actual clutch fillingpressure is all that is required by the empty clutch piston andcylinder.

P is 10 psi (0.7 Atmos.) greater than P1, P1 is equal to P2, P2 is 30psi (2.0 Atmos.) greater than S, S is equal to C, and C is equal toactual clutch fill pressure PA (20 psi or 1.4 Atmos.), according to thecondition illustrated in this figure, with substantial flow through thelarge clutch fill orifice 32 creating a 10 psi (0.7 Atmos.) drop thereinbecause of the large volume of fluid temporarily going therethrough. Aglance for the moment back at FIG. 1 and specifically at extended-lengthdirection lines 56 will make it clear how fluid from direction valvespool 54 can drop 30 psi (2.0 Atmos.) in pressure from P2 to the actualclutch pressure PA by the time it arrives at the selected clutch pistonand cylinder unit F.

The cascading drops in pressures PA, P2 and P1 due to empty piston andcylinder unit F on the line, and the drop in cavity pressure C due tothe precipitous drop of the valve modulated first output pressure P1,results in the residual 270 psi (18.4 Atmos.) signal pressure S forcingthe dump valve piston 174 in the direction of an arrow 210 in FIG. 3 tothe open position causing two coordinated actions. First, the dump valvecontrol edge 182 opens a path from signal pressure chamber 82 throughbore core 180 to drain D, reducing the signal pressure S to about 20 psiand allowing the load piston 164 under force of the spring group 88 toreset leftwardly in the direction of the arrow 166. Second, the dumpvalve land 202 vents fluid from the piston cavity 200 and the passage206 from the back of the piston and bore core 204, through the bore core180 thence to drain D, enabling the approximately 20 psi cavity pressureC to move the piston 194 in the leftward direction of the arrow 201against the minor resistance of the light piston spring 208.

So, contemporaneously with only the major first part of clutch fill, thesimulated clutch fill piston 194 makes a complete control stroke,enlarging the volume of the differential pressure chamber 80 at a fairlysteady rate against the opposition of the light spring 208 within thepiston head. At the same time, fluid flow in the valve output connection38 at pressure P1 will restrictedly enter the differential pressurechamber 80, through appropriate admission means such as through a hole212 at the back of the dump valve 174, at reduced pressure. As a matterof practice, the cavity pressure C and the signal pressure S aresubstantially equal, with the latter pressure S (about 20 psi) beingonly enough the higher of the two by the minor amount necessary to keepthe light valve spring 190 under compression and the dump valve 174hydraulically held open throughout clutch fill. Flow at this timethrough the timing orifice 186 is essentially zero.

Under the favorable clutch fill condition just outlined, the load piston164 will execute a complete resetting stroke contemporaneously with onlythe major first portion of clutch fill time, balanced against theexisting 20 psi signal pressure, the spring group 88 will relax exceptto the extent of transmitting an equivalent of 20 psi (1.4 Atmos.)pressure, and the modulating valve 58 will be modulating the linepressure P in the range of 50 psi (the curve segment identified by thelength of fill interval "FI," FIG. 9, equivalent to (3.4 Atmos.) or 60psi (4.1 Atmos.) or so.

MOTION TO END FILL--FIG. 4

Toward the end of clutch fill, the load piston 164 as shown in thisfigure will have taken its extreme position of full reset and, occurringat or just after clutch fill, the simulated clutch piston 194 willaccording to this showing have completed its control stroke. Inherentlywith the ending of clutch fill, flow through the clutch fill orifice 32,not shown, drastically reduces, the pressure drop thereacrossdisappears, and the valve modulated first output pressure P1 and secondoutput pressure P2 increase about 10 psi immediately (along curvesegment 234, FIG. 9) to the pump line pressure of, say, 60 psi. The dumpvalve 174 in its open-dump position illustrated becomes mechanically andhydraulically unbalanced from the spring force at 190 as augmented bythe rise in pressure to 60 psi (4.1 atmos.) in the P1 connected hole 212leading to the back of the valve 174. The valve 174 at end of filltherefore shifts out away from the adjacent end of bore 34 as closed byhousing 26 and to the right in the direction of the arrow 178 into theclosed-seated position, causing two actions.

First, the dump valve land 202 immediately equalizes pressure across thesimulated clutch piston 194, effecting a bypass around it in a path fromthe back of the piston 194, through the line 206 and bore core 204,through the gap past a stop tang on the end of the valve, through thespace between the valve 174 and the fixed sleeve 188, and thence intothe differential pressure chamber 80 to which the head of the piston 194is exposed. Second, the valve sealing edge 182 seals off the drain borecore 180 from the signal pressure chamber 82 and, via a fill pathincluding the timing orifice 186 forming a first means of connection tothe signal pressure chamber, flow of fluid commences from thedifferential pressure chamber 80 into the lower, 20 psi pressure S ofthe signal pressure chamber 82, to increase pressure S. So by thismeans, a first branch source of the fluid system output leading fromconnection 38, via an interconnection such as an interconnecting housingconnection 213a (FIG. 1), and chamber 80, supplies the signal pressurechamber 82 in the indicated way through orifice 186 (FIG. 4).

Immediately, hydraulic pressure on the load piston 164 will make itspresence felt by moving the latter rightwardly as viewed in FIG. 4, soas to establish starting pressure for the desired pressure rate of risein the affected clutch, as can be understood from FIG. 5.

RATE OF RISE, STARTING PRESSURE--FIG. 5

With the valve parts in position as illustrated for this condition, theunopposed light piston spring 208 will expand and start the simulatedclutch fill piston 194 in the direction of the arrow 196 to reset thepiston against the stop pin 198. Also, the rising signal pressure S willabout simultaneously increase its force and start the load piston 164 inthe direction of the adjacent arrow on its load stroke.

At outset of movement of the load piston 164 on its load stroke,compression will increase in the relatively relaxed spring group 88,communicating itself to the modulating valve 58 and causing the valveland 90 to commence restricting outflow from the bore core 92 whichcarries pump line pressure P. There thus begins a linear rise ofpressure P and, proportionately, a linear rise of the pressures P1, P2,S, C, and PA.

Therefore, as the piston 194 in FIG. 5 completes its resetting strokeand the load piston 164 completes its load or control stroke, the spring104 maintains a continuous 30 psi differential of the linearly risingpressures C, P1, and P2 above signal pressure S, the differentialpressure across the timing orifice 186 remains constant at 30 psi, theflow rate through the orifice 186 remains constant throughout thepressure rate of rise, and the rate of movement of the piston 164 staysconstant throughout the linear pressure rise, which occurs at constantrate for each load or control stroke of the piston 164. That is to say,for a given stroke the rate of rise of pressure does not change althoughthe rate for one stroke may differ from other strokes for reasonshereinafter set forth.

LOAD PISTON--FIG. 6

The referred to uniplanar four spaced control edges about the crown ofthe load piston 164 form part of eight consecutive outside portionsthereof, alternate ones of which are the same flats 214 defining thesealing control edges 170, and each remaining one of which is a land 216retaining its original cylindrical shape and being identical to theother three lands.

The four sealing edges 170 control the bore ports 172 constituting drainholes and, in practice, the drain holes as superimposed in FIG. 6subtend a central angle slightly in excess of the arcuate width,measured in a circumferential direction, of each of the lands 216.Irrespective therefore of the rotative position of the load piston 164in bore 34, not shown, one sealing edge 170 will have a bore port 172aligned in its path of reciprocation so that, by unblocking same, thesealing edge 170 concerned will determine the end of travel of the loadpiston 164 on each load stroke at the same point essentially.

Hydraulic balancing or centering grooves 218 are formed at spacedlocations in the exterior of the load piston 164 adjacent its open end.

RATE OF RISE CRUVES--FIG. 7

Without provision for my novel arrangement just described, clutchpressure at the end of fill can be substantially high due to incompleterecycling of the load piston, not shown, as illustrated by the brokenline rise curve 220 in this figure. That is to say, the end of fillpoint 222 on the curve 220 represents a residual 100 psi (6.8 Atmos.)pressure, and the modulated rate of rise will thus start off at too higha level to effect clutch engagement properly. Under my novelarrangement, however, the load piston is ready for a complete controlstroke at the point close to, but always after, clutch fill when thedump valve shifts to the right and the simulated clutch piston startsresetting movement back to its starting position; then, the rate of riseproceeds in the desired way along the solid line rise curve 224. The endof fill point and piston bottoming are shown for convenience ascoinciding at 226 on the curve 224 and that point represents the desired60 psi (4.1 Atmos.).

SPECIAL APPLICATION--FIG. 1

In one physically constructed embodiment of the invention, the rate ofrise valve 58 had a design of substantial size to be useable withtransmissions of the larger commercial sizes. For application to suchlarger sized transmissions, which can be considered a specialapplication, the connection 213a is shown in FIG. 1 as a single-legconduit component, which properly handles both egress and ingress offluid for the respective open-dump and closed-seat directions ofmovement of the associated dump valve 174. So no restriction means areadditionally necessary or auxiliary fluid handling means areadditionally necessary in controlling speed of movement of the dumpvalve 174. Therefore, the third branch source of system fluid output forchamber 80 as illustrated in FIG. 1 is unnecessary, and a valve 48 tochamber 80 interconnection 221 as shown in the housing 26 can readily beeliminated, preferably so.

GENERAL APPLICATION--FIG. 2

When a design of a rate of rise valve 58 of such substantial sizementioned is applied more generally, suitable as well for smallertransmissions having quickly filled, small clutch cylinders, the lengthof the time periods during a shift cycle are necessarily altered; thesequences change phase somewhat and certain structural modifications arefound to prove beneficial.

As an example, the selected clutch cylinder comparatively fills veryfast, with the result that the modulation bore restriction flow at 32stops relatively prematurely and the first output pressure P1 quicklyrises about 10 psi (0.7 Atmos.) to reach the pumpline pressure P atwhich the pressure P1 stays. Such pressure fluctuation occurs with theload piston 164 still resetting itself and with the clutch simulatingpiston 194 still negotiating and being only partway along in thedirection (leftwardly as viewed in FIG. 2) of its control stroke. So thefill cycle in effect continues for a while as the simulated clutchpiston 194 and piston 164 keep moving, even though the clutch itself isalready filled.

Also, without the structural modification referred to, the dump valvewill tend to more fairly unrestrainedly to the closed-seated positionimmediately upon termination of the fill cycle as caused when thesimulated clutch piston 194 bottoms out at end of its control stroke. Atthat point, essentially where modulation starts, the signal pressure Swill tend to undergo an unwanted pressure rise of the order from perhaps45 psi (3.1 Atmos.) to 65 psi (4.4 Atmos.) rather abruptly; in a smallervehicle equipped with a smaller transmission as referred to, thestart-up of the vehicle from a stopped position will sometimes be lesssmooth than desirable, because of a consequent slight jerky clutchengagement.

Accordingly, as modified for the more general purpose application, theinterconnecting housing connection 213b is illustrated as a two-legconduit component in FIG. 2, wherein a lower leg 223 thereof is shownhydraulically in parallel with an upper leg 225 incorporating acalibrated restriction 227. Then at or about the outset of modulation asdetermined by the bottoming out of simulated clutch piston 194, thecomparatively slow, thus restricted flow from the first branch source ofthe connection 38 to the differential chamber 80 will more graduallymove the dump valve 174 to the closed-seated position and thus impart arise in pressure S of only the order from perhaps 45 psi (3.1 Atmos.) toonly about 50 psi (3.4 Atmos.); regular modulation then raises thepressure linearly and the vehicle starts up without discernible jerk, inthe desired way.

The restriction 227 necessitates two minor adjuncts as preventatives.

One adjunct is the housing connection 221 to prevent the problem of thedump valve 174 floating and sometimes failing to complete itsclosed-seated stroke when vehicle direction changes are made in 2d or 3dgear setting. My solution is that the connection 221, on one side andthe connection 122 on the other side of the dump valve 174 tendimmediately to equalize the pressures fed thereto by the speed valve 48(not shown) when in 2d or 3d gear, so that the dump valve spring 190will unopposedly cause the dump valve to continue its movement oncestarted, into the closed-seated position as desired. The equalization isbrought about because the speed spool land 120, on reaching speed 2position or passing therethrough to speed 3 position, uncovers the mouthof the connection 221 at the same time at which, and in the same way inwhich, it uncovers the mouth of the first auxiliary passage 122 aspreviously described.

The other adjunct, appearing in the lower leg 223, is an interposedspring loaded, ball check valve 229 to prevent any noticeable delay ofthe dump valve 174 in moving to dump position. Therefore, "dumping" ofthe dump valve to the left as viewed in FIG. 2 displaces oil, forcingthe valve 229 to uncheck and unseat, and readily dumping oil throughlower leg 223 toward the lowered pressure P1 in the connection 38 thenleading to an empty clutch.

ACTUAL PRACTICE--FIG. 8

To this point, a diagrammatically shown two-leg component has beendescribed. But in actual practice the general purpose application,modifications hereof will be accomplished with simply a valve 48 andchamber 80 connection 221 and with interposition of a simple flow-checkvalve 231 in a single-leg conduit component serving as the connection213c. After the fashion of the conventional flowcheck, compactarrangement, the outwardly unseating, spring pressed ball check 233 ofvalve 231 has its seat accurately drilled with a calibrated restriction235. So dumping of the dump valve, not shown, is attended by theoutward-opening ball check 233 opening by leaving its seat, with therestriction 235 being ineffective. But flow in the opposite directioncauses the ball check 233 to remain seated or to seat toward the dumpvalve, not shown, whereas flow through the seat restriction 235 controlsclosing of the dump valve with desired slowness.

The valve 48 to chamber 80 interconnection 221 is retained as before, tofacilitate 2d and 3d gear shifts.

DIRECTION SHIFT WHILE IN 2D GEAR SETTING--FIGS. 7, 1, 2

While the end-of-fill point is critical insofar as pressure isconcerned, the previously described shorter rate of rise interval I1 isnot in and of itself undesirable. That is to say, the desired rate ofrise interval I2 indicated in FIG. 7 may be effectively shortened in amanner now to be described, without sacrifice of a smooth clutchengagement.

Instead of conforming to the curve 224 in FIG. 7, the pressure tracewill desirably have a steeper straight slope than shown by the curve 224when a direction change is made while the transmission 10, not shown,remains in second gear. That is, in the higher speed gear compared withfirst gear, a speed clutch change is not felt so abruptly; hence thespeed clutch can go into engagement smoothly at a relatively higherconstant rate of rise of pressure, and the interval I2 will consequentlybe shorter.

In FIG. 1, the speed valve spool 48 in the way described has the speed 2position wherein the spool land 120 uncovers the mouth of the firstauxiliary passage 122 which is in reality an orifice. Such orificeprovides a second means of connection to the signal pressure chamber 82,supplementing the timing orifice flow described already as the firstmeans of connection to the signal pressure chamber 82.

In FIG. 2, the orifice formed by the first auxiliary passage 122communicates restricted flow through a gallery into a bore core 228,thus feeding the signal pressure chamber 82 and establishing a newlarger fixed rate of flow whereby the load piston 164 moves on loadstroke at a faster constant rate, for a correspondingly shorter periodof linear rate of pressure rise of both the signal pressure S and thevalve modulated first output pressure P1. So the rate of rise intervalI2 earlier described will be shorter but will cover the same full rangeof pressure, namely, from roughly 60 psi (4.1 Atmos.) as previously to300 psi (20.4 Atmos.) as previously.

SHIFT INTO THIRD GEAR--FIG. 2

When the transmission 10, not shown, is upshifted into third gear, thesubsequent rate of rise in pressure following fill will be establishednot only as described, by the first and second means of connection tothe signal pressure chamber 82, but also by a third means of connectionconsisting of the second auxiliary passage 124 which is more or lessunrestricted and which communicates essentially the full pressure P1through a gallery and into the bore core 228 which feeds the signalpressure chamber 82. Although the end points of the rate of rise curve224, not shown, have the same pressure ordinates at start and finish,the slope is made much steeper and the constant rate of pressure rise isan appreciably larger figure. In other words, a shift when speed 3 isinvolved can be made both rapidly and smoothly, albeit in the shortestrate of rise interval I2.

SPEED CHANGE IN SAME RANGE--FIG. 1

Speed changes such as the foregoing can be made from among the selectedones of the piston and cylinder units 1, 2, or 3 without disturbing thedirection valve spool 54, which can be left remaining in the forwardposition F, for example, as shown in FIG. 1.

Hence, the clutch filling process will involve only the selected speedclutch, and the clutch F will remain filled during the change speed.

SHIFT CYCLE PRESSURE CURVES--FIG. 9

The solid line curve 230 represents the pressure trace for valve outputP1 and also valve output pressure P2 during a full cycle. The brokenline curve 232 represents the signal pressure S trace for the samecycle.

Following the pressure drop of both pressures at the outset of a shift,represented as essentially vertical straight lines at the extreme left,the simulated clutch fill piston 194, not shown, insures an approximate30 psi differential of the pressure P1 over the signal pressure S duringthe immediately ensuing fill interval F1.

Following fill, the sharp 10 psi pressure rise reflected at 234 in thesolid line curve 230 and reflected at 236 in the broken line curve 232is due to the sudden drop in flow upon filling of the clutch involved.That is, both pressures rise by about the amount of pressure rise acrossfill orifice 32, not shown, which no loner will generate any appreciabledrop thereacross.

The major portions of the curves 230 and 232 representing the modulatedlinear rates of rise of pressure and also those horizontal portionsrepresenting the equilibrium time E1 at full clutch pressure show aconstant differential of about 30 psi between the pressures P1 and S dueto the equivalent 30 psi mechanical compression residual in themodulation valve spring 104, FIG. 2.

SIMULTANEOUS SHIFT--FIG. 8

In a shift requiring that the transmission go from a condition of, forinstance, R1 to F2, both the speed spool 48 and the direction spool 54,not shown, are newly positioned and newly detented in their respectivenew positions. The piston and cylinder unit F and also the piston andcylinder unit 2 require filling, so that the normally rather short filltime F will appear on the pressure trace as just about twice as long aninterval as the previous fill time F1 discussed in connection with FIG.8. Otherwise, the rate of rise modulation curves will appear the sameand both clutch engagements will occur in the desired way.

It will be apparent from the foregoing that my novel arrangement makesthe scheduling function independent of the variables of the system suchas line resistance, pressure drop, and clutch piston displacement. Sothe starting rise pressure will always be at a reduced level in thescheduling cycle and smooth clutch engagement will be assured. Almost assoon as the clutch cylinder or cylinders complete filling each time, thedump valve will shift rightwardly as shown in the drawings into fullyclosed position, and the simulated clutch piston after bottoming willreset rightwardly to its starting position as viewed in the drawings,all ready for the next shift. In effect the piston 194 located insidesleeve 188 within the dump valve cavity, FIG. 5, is like a small clutchpiston being subjected to an equal or at least an equivalent pressureduring clutch fill as the clutch of the selected group or clutches ofthe selected groups are being likewise subjected. Therefore despite itsrelative hydraulic remoteness to the latter, the rate of rise valveassembly in housing 26 essentially knows the actual clutch pressure PAbecause PA is artificially approximated close-by, by the level of cavitypressure C in the differential chamber 80.

What is claimed is:
 1. A rate of rise hydraulic system having aconnection to individual lines of a piston-type, transmission-clutchgroup, wherein the fluid output of the system undergoes pressure loss toan actual clutch fill pressure in order to pass from said connectionthrough said individual lines to reach a selected clutch piston, saidhydraulic system comprising:a clutch pressure modulating valve andsignal pressure control means both reciprocally mounted and in oppositeends of a bore (34) formed by a valve housing, said clutch pressuremodulating valve being arranged to afford flow of the system fluidoutput to said connection, out of pumped fluid supplied thereto from apump source; said signal pressure control means comprising a dump valvemember (174) reciprocally movable in an open-dump direction in toward,and in a closed-seated direction outwardly from, the adjacent end of thebore, and a differential pressure chamber defined between and by thedump valve member and said bore end and receiving system-output-fluidfrom said connection; said dump valve member cooperating with modulatorloading means in said bore to define a signal pressure chamber; aselector valve member 48 disposed in said housing at said connectionhaving spool valve portions effective in progressive selector valvepositions for cooperating with said individual lines to direct systemfluid output to selected ones of the clutch pistons; and first (186) andsecond (122) means of connection from the dump valve member and selectorvalve member, respectively, utilizing system fluid output therefrom tosupply rising signal fluid pressure to the fluid inside the signalpressure chamber.
 2. The invention of claim 1,said second means ofconnection comprising an orifice (mouth of 122 or 124) in said housingin communication with said signal pressure chamber (82) and opened byone of said spool valve portions (120) as the selector valve memberprogresses from one position to another so as to increase flow of thesignal pressure fluid supplied.
 3. The invention of claim 2,saidmodulator loading means comprising biasing means (88) connected at oneend to the clutch pressure modulating valve, 58 and a first piston 164confronting said dump valve member, said first piston 199 connected tothe other end of the biasing means and movable in the bore to load theclutch pressure modulating valve in response to rising signal pressurefor affording a rate-of-rise on the system fluid output pressure; and asecond piston movable in a bore in the differential pressure chamber 80to temporarily enlarge the volume of the same for affording a pressuredrop to the system-output-fluid received therein.
 4. A rate of risevalve assembly for a piston-operated transmission-clutch system, whereinthe valve assembly fluid output undergoes pressure loss to an actualclutch fill pressure in order to reach an affected clutch piston of thetransmission-clutch system, said assembly comprising:a clutch pressuremodulating valve and signal pressure control means oppositely disposedand both reciprocally mounted in a bore 34 formed by a valve housing,with the clutch pressure modulating valve in a first end and the signalpressure control means in a second end of the bore; a load piston in thebore intermediate its first and second ends, and arranged with thesignal pressure control means to form a signal pressure chamber 82therebetween in the bore; spring means 88 arranged for loadinginteraction between the load piston and said valve; said signal pressurecontrol means including a differential pressure chamber, with asimulated clutch fill piston therein affording an enlargement of volumeof the differential pressure chamber during actual clutch fill; andmeans forming first and second paths leading respectively: firstly, fromthe valve assembly fluid output by way of a flow connection means thenthrough the differential pressure chamber, thence through first means(186) in the signal pressure control means to the signal pressurechamber for causing a control stroke of the load piston against thespring means; and secondly, from the signal pressure chamber thencethrough second means (182) in the signal pressure control means todrain, during the actual clutch fill and corresponding enlargement ofthe differential pressure chamber by the simulated clutch fill pistontherein.
 5. The invention of claim 4, characterized by:the first meansin the signal pressure control means comprising a fixed, timing orifice(186) between the differential (80) and signal (82) pressure chambers.6. The invention of claim 4, characterized by:the second means in thesignal pressure control means comprising a dump valve (174) between thesignal pressure chamber (82) and drain (D), and openable and closeableupon reciprocation of the signal pressure control means.
 7. Theinvention of claim 4, the signal pressure control means characterizedby:a dump valve member (174) forming a side of the signal pressurechamber (82), so as to intervene with respect to both the differentialpressure chamber and the drain D, and having a fixed timing orifice(181) therein forming said first means and a drain valve portion (182)forming said second means.
 8. A rate of rise valve assembly for apiston-type-transmission-clutch system, wherein the valve assembly fluidoutput undergoes pressure loss to an actual clutch fill pressure inorder to reach a clutch piston of the transmission-clutch system, saidassembly comprising:a clutch pressure modulating valve and signalpressure control means oppositely disposed and both reciprocally mountedin a bore (34) formed by a valve housing, with the clutch pressuremodulating valve in a first end and the signal pressure control means ina second end of the bore, said valve being arranged to afford flow ofthe valve assembly fluid output, out of pumped fluid supplied theretofrom a pump source; a load piston in the bore intermediate its first andsecond ends, and arranged with the signal pressure control means to forma signal pressure chamber therebetween in the bore; spring means (88),arranged for loading interaction between the load piston and said valve;said signal pressure control means having a differential pressurechamber, and having first means 186 to transfer timing fluid from thedifferential pressure chamber to the signal pressure chamber for causinga control stroke of the load piston against the spring means, and secondmeans (182) to vent signal pressue to reduced value to reset the loadpiston during actual clutch fill, said differential pressure chamberbeing included in said signal pressure control means and with asimulated clutch fill piston (194) therein movable to achamber-enlarging position affording an enlargement of volume of thedifferential pressure chamber during actual clutch fill; and admissionmeans (212) connected between the valve assembly fluid output anddifferential pressure chamber whereby, during actual clutch fill andcorresponding enlargement of the latter by the simulated clutch fillpiston therein, to admit the valve assembly output fluid to thedifferential pressure chamber at reduced pressure equivalent to signalpresure, effectively equalizing pressure across the signal pressurecontrol means and enabling the load piston to fully reset against theequivalent of actual clutch fill pressure.
 9. The invention of claim 8,the signal pressure control means characterized by:a dump valve member(174) forming a side of the signal pressure chamber 82, so as tointervene with respect to both the differential pressure chamber (80)and the drain (D).
 10. The invention of claim 9, said dump valve member(174) having a pressure equalizing valve portion (202) forming anopenable and closeable bypass (206) between opposite sides of thesimulated clutch fill piston; andmeans 208 biasing the simulated clutchfill piston out of its chamber enlarging position so as to reset thepiston to a minimum volume position when said bypass valve portion opensthe bypass 206 and equalizes pressure between opposite sides of thesimulated clutch fill piston.